Such a roentgen lithography apparatus has been built more than five years ago as an experimental apparatus. This is described in DE-OS 25 54 693. As a target material tungsten was used, a material of high atomic number and high melting point. In the electron gun there was a glow cathode comprising a tungsten filament. With this roentgen tube there was produced long wave roentgen radiation which is especially suitable for roentgen lithography, because like the visible and ultraviolet light used up to now, it is absorbed or reflected by selected areas of the usual lithographic masks. These masks are usually provided with thin layer of gold which is able to absorb and to reflect such radiation.
Such roentgen lithography apparatus has not displaced from the market lithography apparatus working with light, although lithography apparatus working with light has very serious disadvantages, in particular a very long exposure time. This lithography apparatus is used in the production of integrated circuits, in particular high integrated and ultra-high integrated circuits. Through the enormous improvement in the use of electronic switching in all technical areas in particular for the control and computation of technical processes, there is an enormous need for simple and rapid production of such integrated circuits. Hence the technique has sought for many years a possibility of making sharp copies of the finest structure in the submicrometer range by means of roentgen rays. From theoretical considerations roentgen rays are especially suitable for this but in practice there has not yet been produced apparatus which safely and dependably can accomplish the required sharp copies in lithography apparatus.
Compared with light optical processes, roentgen processes have the physical advantage that even in the order of magnitude smaller than .mu.m, roentgen ray diffraction and interference are negligible and that consequently in the sub-micrometer region precise silhouettes are to be expected of interposed masks. Dirt and dust play a much lesser role with roentgen rays than with light projection. In contrast with electron optical processes, external electrical interference fields can be neglected.
Because hard roentgen rays can penetrate lithography masks practically unhindered, it is necessary for the production of high contrast images to use weak roentgen rays produced with a voltage from 3 to 25 KV. However with roentgen (retarded-) rays the efficiency of the roentgen ray output is extremely limited. This leads to long exposure time.
On account of these unsuccessful endeavers to work with roentgen retarded rays in lithography, research was undertaken to produce roentgen rays in sufficient yield with the help of a synchroton and novel plasma sources. However because of the high purchase price of a synchroton, the very high operating cost and very great amount of space required for installation of a synchroton, the use of synchrotons for lithography is never commercially economic. Novel plasma sources, on the other hand, are not yet out of the experimental field and are probably scarcely usable on account of the very extensive safety precautions required.
Even positron storage rings have been tried experimentally for roentgen lithography. However these endeavors have not proceeded beyond the experimental state.
There thus remains the problem of creating operational roentgen lithography apparatus.